I need help with this problem..
Problem: A pair of flat, horizontal parallel aluminum plates 100 cm 50 cm has a 1.1 mm vacuum gap between them. How should they be charged if there is to be a uniform upward E-field of 1150 N/C in the gap?
So I figured I could use deltaV=Ed and plug 1.1 mm in for d and 1150 in for E and set it equal to V=kq/r to find q (using r from the area somehow?) but I get the wrong answer and can't figure it out. Help, please!! Thanks!
Problem: A pair of flat, horizontal parallel aluminum plates 100 cm 50 cm has a 1.1 mm vacuum gap between them. How should they be charged if there is to be a uniform upward E-field of 1150 N/C in the gap?
So I figured I could use deltaV=Ed and plug 1.1 mm in for d and 1150 in for E and set it equal to V=kq/r to find q (using r from the area somehow?) but I get the wrong answer and can't figure it out. Help, please!! Thanks!
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Your first approach is correct. V = E*d = 1.1e-3 * 1150 = 1.265V
However, use a different question for the charge stored since this problem relates to capacitance.
C = ε A/d
Q = CV = ε V A/d
Here ε is the permittivity of vacuum, A is the area of the plate, d is the separation and the V is the voltage you calculated.
Q = 8.85e-12 * 1.265 * (1*0.5) / 1.1e-3 = 5.09e-9 C
Now you want to generate a uniform electric field upward, so you want to store Q on the bottom plate. So apply 1.265 V on the bottom plate.
However, use a different question for the charge stored since this problem relates to capacitance.
C = ε A/d
Q = CV = ε V A/d
Here ε is the permittivity of vacuum, A is the area of the plate, d is the separation and the V is the voltage you calculated.
Q = 8.85e-12 * 1.265 * (1*0.5) / 1.1e-3 = 5.09e-9 C
Now you want to generate a uniform electric field upward, so you want to store Q on the bottom plate. So apply 1.265 V on the bottom plate.